from queue import Queue

n, m = input().split()
n = int(n)
m = int(m)

x1, y1 = input().split()
x1 = int(x1)
y1 = int(y1)
x2, y2 = input().split()
x2 = int(x2)
y2 = int(y2)

g = [0] * (n * m)

for i in range (n * m):
    g[i] = []

for i in range(n * m):
    g[i] = []

pole = [0] * n

for i in range(n):
    pole[i] = input()

for i in range(n):
    for j in range(m):
        if (i + 1 < n and pole[i + 1][j] != 'X'):
            g[i * m + j].append((i + 1) * m + j)
        if (i - 1 > -1 and pole[i - 1][j] != 'X'):
            g[i * m + j].append((i - 1) * m + j)
        if (j + 1 < m and pole[i][j + 1] != 'X'):
            g[i * m + j].append(i * m + j + 1)
        if (j - 1 > -1 and pole[i][j - 1] != 'X'):
            g[i * m + j].append(i * m + j - 1)
        #print(i * m + j, g[i * m + j])

used = [0] * (n * m)
d = [-1] * (n * m)
q = Queue()
q.put(x1 * m + y1)
used[x1 * m + y1] = 1

while (not q.empty()):
    v = q.get()

    for i in range(len(g[v])):
        to = g[v][i]
        if (used[to] == 0):
            used[to] = 1
            q.put(to)
            d[to] = d[v] + 1

if (d[x2 * m + y2] == -1):
    print("INF")
else:
    print(d[x2 * m + y2] + 1)